1. Field of the Invention
The present invention relates to a fuel vapor treatment apparatus in an internal combustion engine and a method thereof, especially to an apparatus and a method for estimating a concentration of fuel vapor purged from a canister.
2. Related Art of the Invention
Heretofore, a fuel vapor treatment apparatus is well known, which includes a canister for adsorbing and collecting therein fuel vapor generated in a fuel tank, a purge pipe for supplying the fuel purged from the canister to an intake air collector in an engine, and a purge control valve disposed in the purge pipe for controlling a purge air quantity (Japanese Unexamined Patent Publication No. 7-317582).
The Japanese Unexamined Patent Publication No. 7-317582 also discloses a construction that a fuel vapor inflow quantity sucked into the engine is calculated based upon a mean value of an air-fuel ratio feedback correction value and a fuel injection quantity of a fuel injection valve is corrected corresponding to the fuel vapor inflow quantity.
However, since a detection delay of the fuel vapor inflow quantity to the engine is large in the above apparatus, the correction of the fuel injection quantity is delayed and an air-fuel ratio of the combustion mixture deviates greatly from a target value, resulting in deterioration of exhaust emission.
Further, there has been a problem in that if a control gain of the purge air quantity is lowered in order to suppress an occurrence of the air-fuel ratio deviation due to the detection delay, a treatment of fuel vapor cannot be sufficiently promoted.
The present invention has been achieved in view of the foregoing problems, and has an object of providing an apparatus and a method capable of estimating a fuel vapor concentration in a good response, so that an air-fuel ratio can be maintained in the vicinity of a target air-fuel ratio and a treatment of fuel vapor can be promoted well.
In order to achieve the above object, with the present invention, the construction is such that a fuel vapor concentration in purge air is estimated based upon the purge air that is purged from a canister for adsorbing and collecting the fuel vapor, and is supplied to an intake system of an engine through a purge pipe and a purge control valve, an intake air amount of the engine, a fuel injection quantity to the engine, and an air-fuel ratio of the combustion mixture.
With this construction, by correcting a control signal output to the purge control valve based upon the concentration of the fuel vapor estimated as in the above, the purge air quantity is corrected corresponding to the concentration of the fuel vapor.
More specifically, a target purge rate is corrected based upon the estimated value of the fuel vapor concentration and a control signal in response to the corrected target purge rate is output to the purge control valve.
The fuel injection quantity to the engine may be corrected instead of correcting the purge air quantity controlled by the purge control valve.
The other objects, features of this invention will become understood from the following description with reference to the accompanying drawings.